The glass industry has developed several products for use as automotive and architectural glazings, having low transmittance values in order to admit some light but exclude much of the solar energy from the interior of the automobile or building. One method for producing such products has been to include large quantities of iron in the glass, thereby producing a bluish-green glass which absorbs infrared energy and ultraviolet radiation. An alternative method of producing a product having low transmittance has been to coat glass or plastic substrates with metallic or metallic oxide layers, which absorb or reflect certain wavelengths of solar radiation. Such coatings may be deposited by several well known methods, including such as for example thermal evaporation, chemical vapor deposition, sputtering, etc. A particularly useful method for applying solar control films to transparent substrates is disclosed in U.S. Pat. No. 3,673,981 to Beckham et al.
A major disadvantage inherent in the coated transparent substrates of the prior art is the high film side reflectance resulting from the deposited film layers. In particular, automobile manufacturers require the lowest possible interior film side reflectance, especially for curved automotive solar control glazings, in order to minimize their so called "funhouse mirror" effect. The coated glass panels heretofore known in the art as useful for solar control windows in vehicles have typically exhibited visible light transmittance values in the range of about 10%, and film side reflectance values of at least 35%.
U.S. Pat. No. 3,826,728 discloses a transparent glass panel coated with consecutive layers of nickel or a nickel-based alloy, sputter coated to a thickness from 50 to 400 Angstroms, and a protective metal oxide such as silicon dioxide having a thickness from 1,000 to 100,000 Angstroms. The disclosed coating reduces infrared energy transmittance, and therefore total solar energy transmittance, but allows the transmittance of some visible light. Also disclosed is a single 80 Angstroms thick coating of chromium on one-eighth thick window glass. The patent suggests that chromium is an undesirable coating material, because it allows increased transmittance of infrared energy at increasing wavelengths.
U.S. Pat. No. 4,022,947 discloses a transparent panel, which allows visible light transmittance from 6% to 20%, and exhibits a film side reflectance from 42% to 60%. The transparent panel comprises consecutively a transparent substrate such as glass, a 30 to 600 Angstrom thick sputtered metal film containing predominantly iron, nickel, and chromium, and a 100 to 3,000 Angstrom thick sputtered protective overcoat of an oxide of a metal mixture or alloy containing predominantly iron, nickel, and chromium. Such a transparent panel would not be desirable as a solar control vehicle window, however, because film side reflectance values are 42% or greater.
It would be desirable to produce a transparent panel, for use as an automotive or architectural solar control glazing, having a visible light transmittance less than 10% and a film side reflectance less than 30%.
It must be noted that the prior art referred to hereinabove has been collected and examined only in light of the present invention as a guide. It is not to be inferred that such diverse art would otherwise be assembled absent the motivation provided by the present invention.